The ornamental design for an electric clamp apparatus, as shown and described.
FIG. 1 shows a front view of an electric clamp apparatus showing our new design;
FIG. 2 shows a rear view thereof;
FIG. 3 shows a right side view thereof;
FIG. 4 shows a left side view thereof;
FIG. 5 shows a top view thereof;
FIG. 6 shows a bottom view thereof;
FIG. 7 shows a top, front and right side perspective view thereof;
FIG. 8 shows a top, front and right side perspective view thereof in alternative position; and,
FIG. 9 shows a top, front and right side perspective view thereof in alternative position.
The broken lines in FIGS. 6 and 9 are included for the purpose of illustrating portions of the electric clamp apparatus that form no part of the claimed design.